Ionic Compatibilization of Polymers.

The small specific entropy of mixing of high molecular weight polymers implies that most blends of dissimilar polymers are immiscible with poor physical properties. Historically, a wide range of compatibilization strategies have been pursued, including the addition of copolymers or emulsifiers or installing complementary reactive groups that can promote the in situ formation of block or graft copolymers during blending operations. Typically, such reactive blending exploits reversible or irreversible covalent or hydrogen bonds to produce the desired copolymer, but there are other options. Here, we argue that ionic bonds and electrostatic correlations represent an underutilized tool for polymer compatibilization and in tailoring materials for applications ranging from sustainable polymer alloys to organic electronics and solid polymer electrolytes. The theoretical basis for ionic compatibilization is surveyed and placed in the context of existing experimental literature and emerging classes of functional polymer materials. We conclude with a perspective on how electrostatic interactions might be exploited in plastic waste upcycling.

Aqueous Formulation of Concentrated Semiconductive Fluid Using Polyelectrolyte Coacervation.

Conjugated polyelectrolytes (CPEs), which combine π-conjugated backbones with ionic side chains, are intrinsically soluble in polar solvents and have demonstrated tunability with respect to solution processability and optoelectronic performance. However, this class of polymers often suffers from limited solubility in water. Here, we demonstrate how polyelectrolyte coacervation can be utilized for aqueous processing of conjugated polymers at extremely high polymer loading. Sampling various mixing conditions, we identify compositions that enable the formation of complex coacervates of an alkoxysulfonate-substituted PEDOT (PEDOT-S) with poly(3-methyl-1-propylimidazolylacrylamide) (PA-MPI). The resulting coacervate is a viscous fluid containing 50% w/v polymer and can be readily blade-coated into films of 4 ± 0.5 µm thick. Subsequent acid doping of the film increased the electrical conductivity of the coacervate to twice that of a doped film of neat PEDOT-S. This higher conductivity of the doped coacervate film suggests an enhancement in charge carrier transport along PEDOT-S backbone, in agreement with spectroscopic data, which shows an enhancement in the conjugation length of PEDOT-S upon coacervation. This study illustrates the utilization of electrostatic interactions in aqueous processing of conjugated polymers, which will be useful in large-scale industrial processing of semiconductive materials using limited solvent and with added enhancements to optoelectronic properties.

The Role of Backbone Polarity on Aggregation and Conduction of Ions in Polymer Electrolytes.

The usual understanding in polymer electrolyte design is that an increase in the polymer dielectric constant results in reduced ion aggregation and therefore increased ionic conductivity. We demonstrate here that in a class of polymers with extensive metal-ligand coordination and tunable dielectric properties, the extent of ionic aggregation is delinked from the ionic conductivity. The polymer systems considered here comprise ether, butadiene, and siloxane backbones with grafted imidazole side-chains, with dissolved Li+, Cu2+, or Zn2+ salts. The nature of ion aggregation is probed using a combination of X-ray scattering, electron paramagnetic resonance (in the case where the metal cation is Cu2+), and polymer field theory-based simulations. Polymers with less polar backbones (butadiene and siloxane) show stronger ion aggregation in X-ray scattering compared to those with the more polar ether backbone. The Tg-normalized ionic conductivities were however unaffected by the extent of aggregation. The results are explained on the basis of simulations which indicate that polymer backbone polarity does impact the microstructure and the extent of ion aggregation but does not impact percolation, leading to similar ionic conductivity regardless of the extent of ion aggregation. The results emphasize the ability to design for low polymer Tg through backbone modulation, separately from controlling ion-polymer interaction dynamics through ligand choice.

Using A Spin-Coater to Capture Adhesive Species during Polydopamine Thin-Film Fabrication.

Spin-coating was evaluated as a technique to study events that occur during polydopamine (PDA) thin-film formation. The reaction variants studied included type of oxidant, dopamine (DA) concentration, pH, adhesion time prior to spin, substrate chemistry, and notably, DA solution aging time. A strong oxidant, sodium periodate (SP), and a weak oxidant, atmospheric oxygen were chosen. It was found that reactions in solution were much faster and produced much thicker PDA films with SP than with oxygen. PDA thickness correlated positively with DA concentration, SP solution pH, and adhesion time. DA oxidation and aggregation is a dynamic process, which is reflected in the DA aging-time parameter. PDA film thickness reached a maximum value as DA solution aged. Color photography, UV-vis spectroscopy, and dynamic light scattering indicated that the optimal DA aging time for PDA adhesion is the result of the evolution of PDA particle size and chemistry over time. The capture of the optimal aging-time window was identified as the critical parameter for preparing PDA films with continuity and appreciable thickness. When these conditions were applied in a modified dip-coating method, comparable PDA films were fabricated as those obtained from spin-coating. Native silicon wafers (SiO2) as well as wafers that were modified with polydimethylsiloxane (PDMS) and amine-containing polydimethylsiloxane (PADMS) were chosen to represent a wide range of substrates with different substrate-PDA interactions. The main effect of substrate structural difference was on PDA film morphology. "Island" morphologies were obtained on PDMS where only hydrophobic interactions are responsible for PDA adhesion, while "speck" morphologies were observed on SiO2 and PADMS. The stabilities of the fabricated PDA films were tested in 0.1 M HCl and DMSO. The SP-derived PDA films exhibited very little mass loss compared to those fabricated using either the conventional dip-coating method or oxygen as an oxidant. Choosing a strong oxidant, understanding the DA reaction dynamics, and taking advantage of the optimal DA aging time are important in the fabrication of stable PDA films on a variety of substrates.